/**
 @file
 CRC Computations

 @defgroup util_crc16 "util/crc16.h": CRC Computations
 @code#include "util/crc16.h"@endcode

 This header file provides functions for calculating
 cyclic redundancy checks (CRC) using common polynomials.
 Modified by Doc Walker to be processor-independent (removed inline
 assembler to allow it to compile on SAM3X8E processors).

 @par References:
 Jack Crenshaw's "Implementing CRCs" article in the January 1992 issue of @e
 Embedded @e Systems @e Programming. This may be difficult to find, but it
 explains CRC's in very clear and concise terms. Well worth the effort to
 obtain a copy.

 */
/* Copyright (c) 2002, 2003, 2004  Marek Michalkiewicz
 Copyright (c) 2005, 2007 Joerg Wunsch
 Copyright (c) 2013 Dave Hylands
 Copyright (c) 2013 Frederic Nadeau
 Copyright (c) 2015 Doc Walker
 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:

 * Redistributions of source code must retain the above copyright
 notice, this list of conditions and the following disclaimer.

 * Redistributions in binary form must reproduce the above copyright
 notice, this list of conditions and the following disclaimer in
 the documentation and/or other materials provided with the
 distribution.

 * Neither the name of the copyright holders nor the names of
 contributors may be used to endorse or promote products derived
 from this software without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE. */

#ifndef _UTIL_CRC16_H_
#define _UTIL_CRC16_H_

/** @ingroup util_crc16
 Processor-independent CRC-16 calculation.

 Polynomial: x^16 + x^15 + x^2 + 1 (0xA001)<br>
 Initial value: 0xFFFF

 This CRC is normally used in disk-drive controllers.

 @param uint16_t crc (0x0000..0xFFFF)
 @param uint8_t a (0x00..0xFF)
 @return calculated CRC (0x0000..0xFFFF)
 */
static uint16_t crc16_update(uint16_t crc, uint8_t a) {
	int i;

	crc ^= a;
	for (i = 0; i < 8; ++i) {
		if (crc & 1)
			crc = (crc >> 1) ^ 0xA001;
		else
			crc = (crc >> 1);
	}

	return crc;
}

#endif /* _UTIL_CRC16_H_ */
